I agree, 100%. There is a 410(b) issue. That issue actually jumps out on the first read. I was trying to determine whether or not there was another "hypothetical" issue that would question deductibility.
The title of the original post mentioned 410(b), but the question when on to ask about making the maximum deductible contribution. The deductibility limit is going to increase from $25,000 to $30,000 when you implement the fail safe - or 11(g) amendment to bring the other participant into the 'benefiting' group.
I was trying to address the deductiblity while admittedly ignoring the obvious 410(b) issue; which was more of a theoretical answer than a pragmatic approach to the issue. But, I agree with you 100%.
Good Luck!